Ordinarily, plastic encapsulated IC packages are subjected to electric property tests and a reliability test called a burn-in test prior to shipment in order to distinguish between good and defective products. In an electrical property test, input and output characteristics of the IC chip, pulse properties, noise leeway, and the like, are tested. Those IC packages that pass the electric property test are then subjected to a burn-in test in which they are arranged in an oven and caused to function for a certain period of time at a selected high temperature, for example, 125.degree. C., and under a source voltage which is approximately 20 per cent higher than the rated value. IC packages that fail the burn-in test are discarded as defective products and only those IC packages that continue functioning properly are shipped out as good products.
BGA packages having spherical solder balls arranged on the lower side of the packages in a selected matrix or zigzag fashion are in wide use. This type of package is capable of having an increased terminal pitch with a small outer dimension and is more resistant to damage caused by contact with other parts. FIGS. 6a and 6b show a typical prior art socket used for burn-in tests of IC's such as BGA packages. Socket 101 comprises a plastic (in plan view) rectangular base 102 on which is mounted a horizontally movable slider 103 which receives thereon a BGA package. A frame shaped cover defining an opening 104a, also made of plastic, is received on top of base 102 and is vertically movable relative to the base. The cover is biased in a direction away from the base by means of compression coil springs 105. A through hole corresponding to each solder ball 100a of the BGA package is formed in slider 103 and base 102. A contact member 106 for electrical connection with a respective solder ball 100a of the BGA package is arranged to run through each of the through holes of slider 103 and base 102. Each contact member 106 comprises an elongated metallic member having a pair of arms 106a and 106b provided at one end thereof. Each contact member 106 is fixed in a vertical attitude on base 102, with arms 106a and 106b facing upwardly. Each contact member has a protruding part such as a tab (not shown in the drawing), on one of side by side arms 106a, 106b. Arms 106a, 106b open relative to one another as the tab engages with a partition wall (not shown in the drawing) of slider 103. A sliding mechanism for moving slider 103 in parallel with the bottom of base 102 comprises a pair of generally L-shaped lever member 108 rotatably connected at opposite ends of a shaft 107. Shaft 107 is received in a slot formed at the right side of slider 103 as seen in the drawings. A short arm 108a of each lever member 108 is rotatably connected to a shaft 109 mounted in base 102 thereof at one side (the right-hand side shown in the drawing), installed so that it extends in parallel with shaft 107. A respective lever member 111 is rotatably connected at both ends of a shaft 110 mounted on the opposite side of base 102 and extending in parallel with shafts 107, 109 and the end portion of each lever member 108 is slidably connected in a longitudinally extending slot formed in the middle part of lever members 111 by means of pins 112. The distal tip 11la of lever member 111 engages a protruding part 104b of the top wall of cover 104. Horizontally disposed compression coil springs 113 are placed between base 102 and slider 103 in the vicinity of shaft 110 for biasing the slider in the direction shown by the head of arrow X in FIG. 6b.
In a socket 101 constructed as described above, if cover 104 is pressed down from the position shown in FIG. 6a to the position shown in FIG. 6b, lever members 108 and 111 rotate toward base 102 and shaft 107 moves slider 103 in conformity with the movement of lever member 108, thereby shifting it in the opposite direction from the one indicated by arrow head X. As a result of this, one of the arms, for example, arm 106a of each contact member 106, engages the partition wall of slider 103 and is thereby opened. If, in this state, BGA package 100 is inserted into adaptor 103c of slider 103, each solder ball 100a of BGA package 100 enters the gap between the open arms 106a and 106b of a respective contact member 106. When the downward force on cover 104 is removed, lever members 108 and 111 rise and slider 103 moves in the direction of the head of arrow X by means of the force exerted by compression coil springs 113, closing arms 106a and 106b of each contact member 106 with each solder ball 100a of BGA package 100 held by arms 106a and 106b of a respective contact member 106. As a result of this, each solder ball 100a of BGA package 100 can be electrically connected to a respective contact member 106.
In the case of a prior art socket as described above, however, the linkage mechanism made by lever members 108, 111 and associated shafts used for moving slider 103 requires an increased number and complexity of parts along with an increase in the number of steps and time for assembling the product.
Further, such linkage mechanisms increase the size and weight of the socket itself.